Not Applicable.
Not Applicable.
The present invention relates to an apparatus for determining the shelf-life of foods, and more particularly to a method and device for determining the stability of lipids.
In the food industry, xe2x80x9cshelf lifexe2x80x9d is a term used to describe the length of time a packaged food can be stored without deteriorating to a point that it is inedible due to taste or safety reasons. Many factors affect the shelf life of packaged food products. For example, processing techniques and chemical preservatives affect shelf life, as do moisture content and chemical composition of natural food ingredients. Additionally, almost all food products include one or more fats or lipids in liquid or solid form, the characteristics of which can greatly affect not only the nutritional quality and taste of the food, but also its shelf life.
Polyunsaturated fats, such as walnut oil, flaxseed oil, and fish oil oxidize readily and can become rancid in a few weeks or less, even if refrigerated. Therefore, these oils are almost universally shunned by food processors in favor of refined oils such as cottonseed oil, corn oil, and peanut oil that are hydrogenated or partially-hydrogenated to render them less readily oxidized, and therefore more stable. Although stability characteristics are of considerable importance with respect to edible lipids, they are also important with respect to inedible oils that have commercial applications, wherein the commercial value of the oil is affected by its stability.
All oils and fats have a resistance to oxidation which depends on their degree of saturation, natural or added antioxidants, pro-oxidants or prior abuse. Oxidation is slow until this resistance is overcome, at which point oxidation accelerates rapidly. The length of time before the onset of rapid acceleration is commonly referred to as the xe2x80x9cinduction period,xe2x80x9d or Oxidative Stability Index (OSI).
Instruments have been developed to help gauge or predict the stability of lipids by accelerating the development of oxidative rancidity so that the useful life of a lipid can be determined. Such an instrument for determining oxidative stability is disclosed in U.S. Pat. No. 5,339,254, wherein a lipid is forced to oxidize and the time for oxidation is measured. More specifically, the disclosed instrument works by heating a lipid sample and forcing air through it. Air exiting the oil is subsequently directed into water in which a conductivity sensor is immersed. The sensor measures a change in conductivity of the water caused by volatile, water-soluble materials emitted by the oxidizing oil. The measurement of the length of time that elapses from the start of the test, until the point of maximum change of rate of conductivity in the water, provides the OSI value at a selected temperature, for example: OSI=11.7 hours at 110xc2x0 C.
Although the above-described apparatus and method may be suitable for determining the stability of pure lipids, it is not effective for measuring the stability of lipids which are components of more complex samples, because some of the other components also emit volatile, water-soluble materials that cause a change in conductivity. Thus, the instrument incorrectly identifies the onset of lipid oxidation and provides an unreliable OSI value. Notable among problematic sample types are protein-containing foods which emit volatile, alkaline materials, such as ammonia and a variety of amines, all of which increase water conductivity.
Another deficiency of the known apparatus is the great length of time required to perform a test. For example, typical OSI measurements on salad oils can take about sixteen hours, while hardened oils such as those contained in some margarine formulations can take several hundred hours.
Accordingly, there is a need for an improved method and apparatus capable of accurate measurement of the oxidative stability of lipids, either alone or in addition to other materials, as well as the ability to process and evaluate a sample much more quickly than known devices.
The present invention provides a method and apparatus for accurately predicting the oxidative stability of a pure lipid or a material including one or more lipids in addition to other ingredients. In an exemplary embodiment, a test system includes a first container adapted to contain the sample and a heater for heating the sample to make it give off an effluent gas. A second container contains a collection fluid through which the effluent gas can be passed and one or more sensors within the second container can measure pH, acetate, ammonia, and/or formate levels. An optional computation device in communication with the one or more sensors determines a point in time at which the level of pH, acetate, formate and/or ammonia changes suddenly.
Thus, an exemplary method of predicting material stability includes the steps of: heating a sample of material including a lipid; passing a gas through the heated sample to provide effluent gas; passing the effluent gas through a collection fluid; and testing the collection fluid to determine the level of pH, acetate, formate and/or ammonia. In a subsequent step, a point in time at which the level of one of pH, acetate, formate and/or ammonia changes suddenly is identified.